RecQ helicases have crucial roles in the maintenance of genome stability. In humans, it is known that deficiencies in three of the five human RecQ helicases cause genetic disorders characterized by cancer predisposition, premature aging and developmental abnormalities. These disorders are Bloom's syndrome (BS), Werner's syndrome (WS), and Rothmund-Thomson syndrome (RTS), which are caused by mutations in BLM, WRN and RECQ4, respectively. Despite the apparent structural and biochemical similarities between the BLM, WRN and RECQ4 proteins, the phenotypes of BS, WS and RTS are different, suggesting that each disease pathway is functionally distinct to some extent. BS is characterized by most prominently, a predisposition to all types of cancers. WS is characterized by the premature development of features that resemble aging. RTS is characterized by skin and skeletal abnormalities, signs of premature aging, and cancer predisposition, especially to osteosarcomas. Recent research has shown many connections between all three proteins and the regulation of excess HR (Homologous recombination). It was also indicated that BLM is involved in repair of stalled DNA replication forks, and that WRN is required for telomere maintenance.